Pulsed Electric Field Effects on Wine Yeast in Defined Grape Juice Medium

Abstract

Pulsed electric fields (PEF) processing has been explored as a way to enhance extraction of bioactive compounds owing to its ability to alter cell membrane permeability. In wine making PEF has been used to improve the effectiveness of maceration process, however, little is known about how PEF affects the subsequent composition of the wild yeast population. Such information is required as wild yeast growth, during maceration and early stages of fermentation, can modify the flavor profile of wine. This study investigated the impact of PEF on Saccharomyces cerevisiae, Picchia kluyveri and Hanseniaspora uvarum. Each yeast species (4.3-4.8 Log CFU /mL) was suspended in defined grape juice medium (DM) of pH 3.5 and subjected to PEF treatments of either 15 , 60 or 160 kJ/kg at a field strength of 1.0-1.1 kV/cm. Yeast cell numbers were estimated immediately after PEF treatment and after 1, 2, 3, or 8 days under simulated maceration conditions. S. cerevisiae was the most sensitive species tested, to pH in DM and to the PEF treatments (P 0.05). The numbers of spoilage yeast H. uvarum decreased to below the detection limit of 2.5 log CFU/mL after high PEF treatment and the degree of sub lethal injury was dependent on maceration time and PEF intensity (P<0.05). This study suggests that application of PEF during winemaking can enhance extraction and inhibit spoilage yeast while having a limited effect on the beneficial natural wine yeast.